题解 | 两直线交点

#include <bits/stdc++.h>
#include <iomanip>
using namespace std;
 
struct point {
    double x, y;
    point(double A, double B) {
        x = A, y = B;
    }
    point() = default;
};
 
struct line {
    double A, B, C;
    line(point p1, point p2) {
        A = p2.y - p1.y;
        B = p1.x - p2.x;
        C = p2.x*p1.y - p1.x*p2.y;
    }
    line() = default;
};
 
point findMeetingPoint(line L1, line L2) {
    double A1 = L1.A, B1 = L1.B, C1 = L1.C;
    double A2 = L2.A, B2 = L2.B, C2 = L2.C;
    if (A1*B2 == A2*B1) return {-1, -1};
    return {(B1*C2-B2*C1)/(A1*B2-A2*B1), (A1*C2-A2*C1)/(A2*B1-A1*B2)};
}
 
int main() {
    point A, B, C, D;
    cin >> A.x >> A.y >> B.x >> B.y >> C.x >> C.y >> D.x >> D.y;
    
    line AB = line(A, B);
    line CD = line(C, D);
    
    point ans = findMeetingPoint(AB, CD);
    
    cout << fixed << setprecision(6);
    cout << ans.x << " " << ans.y;
    
    return 0;
}